Sound-damping profiled member

ABSTRACT

Strip ( 3 ) to be inserted between two elements ( 1, 2 ) in order to cause acoustic attenuation of the noise propagating through at least one of the elements, the.strip ( 3 ) being made of at least one plastic-based damping material i, characterized in that the strip ( 3 ) has an equivalent real stiffness per unit length K′ eq  equal to at least 25 MPa and an equivalent loss factor tan δ eq  equal to at least 0.25.

The present invention relates to a strip to be inserted between twoelements in order to cause acoustic attenuation of the noise propagatingthrough at least one of the elements, the strip being made of at leastone plastic-based damping material i.

Such a strip may especially be used for glazing in vehicles,particularly automobiles, for the purpose of improving acoustic comfort.

In automobiles, the sources of discomfiture, of mechanical, thermal,visibility or other origin, have gradually been overcome. However,improvement in acoustic comfort still remains to be achieved.

Aerodynamic noise, i.e. noise created by the friction of the air over amoving vehicle, has, at least in part, been dealt with at its source,that is to say, to save energy, shapes have been modified, thusimproving penetration through the air and decreasing turbulence, whichis itself a source of noise. Among the walls of a vehicle that separatethe external source of aerodynamic noise from the interior space wherethe passengers are, the windows are obviously the most difficult to dealwith. It is not possible to use pasty or fibrous absorbents, that arereserved for the opaque walls, and, for practical reasons or for reasonsof weight, the thicknesses cannot be increased inconsiderably. Europeanpatent EP-B1-0 387 148 discloses glazing assemblies that exhibit goodinsulation against aerodynamic noise without their weight and/or theirthicknesses being increased too greatly. The patent thus provides alaminated glazing assembly whose interlayer has a flexural dampingfactor v=Δf/f_(c) of greater than 0.15, the measurement being carriedout by exciting, by means of a shock, a laminated bar 9 cm in length and3 cm in width of a laminated glass in which the resin is between twothick glass panes, each 4 mm in thickness, and by measuring f_(c), theresonant frequency of the first mode, and Δf, the width of the peak atan amplitude of A/√{square root over (2)} where A is the maximumamplitude at the frequency f_(c) such that its acoustic damping indexdoes not differ, for any frequency greater than 800 Hz, by more than 5dB from a reference index that increases by 9 dB per octave up to 2000Hz and by 3 dB per octave at higher frequencies. In addition, thestandard deviation σ of the differences in its acoustic damping indexcompared with the reference index remains less than 4 dB. Thethicknesses of the two glass panes may be identical and equal to 2.2 mm.That patent thus provides a general solution to the problem of acousticinsulation with respect to the aerodynamic noise of a vehicle.

On the other hand, the treatment of glazing assemblies for protectionagainst solid-borne noise, i.e. against noise transmitted via solids, inthe frequency range from 50 to 300 Hz or even 800 Hz, is more difficultto achieve. This is because it turns out that the use of connectingpieces remains inadequate for avoiding transmission of the noise throughvibration of the glazing. In this regard, it has been found that ahumming noise perceptible to passengers appears at certain rotationspeeds of the engine, thus creating a source of discomfiture. This isbecause the rotation of the engine creates vibrations that aretransmitted, for example, to the bodywork and thus, via a chain effect,to the windows. It is known that the energy acquired by an objectsubjected to a shock causes a vibration phenomenon and that, immediatelyafter the shock, the object, now free again, vibrates in its naturalmode. A vibration frequency is associated with each mode. The amplitudeof the vibration depends on the initial excitation, i.e. on the spectralcomponent of the shock (the amplitude of the shock at the frequencystudied) and on the area of impact of the shock, the modal deformationbeing greater or smaller depending on whether the shock occurs at avibration antinode or at a vibration node.

In order for a natural mode to be excited:

-   (1) the deformation caused at the point of impact must not be at a    vibration node of the mode; and,-   (2) the energy spectrum of the shock must have a component at the    resonant frequency of the mode.

The latter condition is virtually always fulfilled, since a very briefshock has a virtually uniform energy spectrum.

The first condition is also fulfilled and, for a bar free at its endsfor example, all that is required is to tap one of the ends in order toexcite all the modes.

Solid-borne excitation is peripheral and it has been demonstrated that,at certain engine vibration frequencies, that is to say at certainrotation speeds of the engine, the windows and the passenger compartmentof the vehicle each have a vibration mode whose coupling amplifies thehumming that arises from the radiation of noise emanating in this casefrom the engine, via the windows. Of course, the rotation speed of theengine that gives rise to these phenomena is peculiar to each type ofvehicle and thus cannot be generalized to a single value.

Thus, to improve acoustic comfort in the passenger compartment of thevehicle with respect to solid-borne noise, patent EP 0 844 075 proposesa laminated glazing assembly comprising at least one interlayer filmpossessing very satisfactory damping properties as regards audiblesolid-borne sounds, since it has a loss factor tan δ of greater than 0.6and a shear modulus G′ of less than 2×10⁷ N/m², within a temperaturerange between 10 and 60° C.

Another solution may consist in placing around the periphery of theglazing a strip with acoustic damping properties. For this purpose,patent DE 198 06 122 proposes a strip that firstly bonds the pane of thevehicle to the bodywork and also acts as a damper. The strip is hollowand filled with a pasty material whose function is to damp thevibrations, the body of the strip being made of an adhesive materialthat becomes elastic after crosslinking.

However, the latter solution has the drawback that the strip does nothave a stiffness sufficient to guarantee the desired acousticperformance.

Firstly, the strip described, which is a coextruded bead, is designed tobe compressed between the glazing and the bodywork, but this method ofapplication by compression, coupled with the constituent materials ofthe strip, does not guarantee the desired final dimensional shape. Now,after the glazing has been attached to the bodywork by means of saidstrip, it is essential for the dimensions of the strip to be maintainedthroughout the damping performance that it must provide, as we will seein the description of the invention.

Secondly, the pasty material internal to the body of the strip remainssoft and there is no guarantee that it remains confined after thecoextruded bead has been compressed against the bodywork element, sincethe body of the strip formed from the adhesive material is also pastybefore crosslinking, thereby incurring, during deposition of the bead,the risk of the internal pasty material spreading out beyond the body ofthe strip.

The object of the invention is therefore to provide, as acoustic dampingsolution, especially for the glazing of automobiles, a strip that doesnot have the drawbacks of the prior art.

According to the invention, the strip is characterized in that it has anequivalent real stiffness per unit length K′_(eq) equal to at least 25MPa and an equivalent loss factor tan δ_(eq) equal to at least 0.25.

The stiffness is a quantity that relates the deformations of the stripto the forces that are applied to it. The stiffness is defined by therigidity of the constituent materials of the strip and by the geometryof the strip, the rigidity being a quantity characteristic of thematerial, which is a function of the Young's modulus and/or the shearmodulus. In the rest of the description, the formulae given forcalculations will be related only to the Young's modulus—the shearmodulus will not be taken into account, the tensile/compressive stressesand strains related through the Young's modulus being sufficientlyrepresentative.

In a known manner, the equivalent stiffness per unit length K*_(eq) is acomplex number written as K*_(eq)=K′_(eq)+j K″_(eq) with a real partK′_(eq), called in the description the equivalent real stiffness perunit length, and an imaginary part K″_(eq) that corresponds to the lossmodulus, i.e. to the conversion of the deformation energy of the stripinto thermal energy throughout the entire strip.

The loss modulus is defined by${\tan\quad\delta_{eq}} = {\frac{K_{eq}^{''}}{K_{eq}^{\prime}}.}$

To determine the equivalent real stiffness per unit length K′_(eq) andthe equivalent loss factor tan δ_(eq) of a strip formed from one or morematerials, these quantities will be measured using a viscoanalyzer—anapparatus known to those skilled in the art, including acoustics andpolymer experts. The viscoanalyzer measures the equivalent realstiffness k′_(eq) and the equivalent loss factor k″_(eq) of a stripspecimen with a cross section identical to that of the strip and with alength L and then the following are calculated:

-   -   the ratio of the measured equivalent real stiffness to the        length L in order to obtain the equivalent real stiffness per        unit length K′_(eq) of the strip: K′_(eq)=k′_(eq)/L; and    -   the ratio of the measured equivalent loss factor to the measured        equivalent real stiffness in order to obtain the equivalent loss        factor tan δ_(eq) of the strip:        $\frac{k_{eq}^{''}}{k_{eq}^{\prime}}.$

Advantageously, the strip has an equivalent real stiffness per unitlength K′_(eq) of between 30 MPa and 270 MPa and an equivalent lossfactor tan δ_(eq) equal to at least 0.4.

According to a first embodiment, the strip is formed from a singledamping material or from several damping materials, it being possiblefor the damping material or materials to exhibit adhesion propertieswith respect to the two elements.

According to a second embodiment, the strip is formed from at least onedamping material and from a nondamping adhesive material, the adhesivematerial being designed to bond the two elements together.

According to one feature of this second embodiment, the adhesivematerial adheres via two opposed faces to the two elements respectively,the damping material being bonded to at least one of the two elements.

According to another feature, the adhesive material adheres via one ofits faces to the damping material that is bonded to one of the elementsand adheres via its opposite face to the other element to be joinedtogether.

According to another feature, the strip comprises several dampingmaterials placed as a stack of layers one on top of another, each of thematerials at the ends of the stack being bonded to one of the twoelements to be joined together or to the adhesive material.

As a version, the strip comprises several damping materials placed injuxtaposition one beside another, butted together or otherwise, each ofthe materials having two opposed surfaces bonded to the two elements tobe joined together, respectively.

According to yet another version, the strip comprises several dampingmaterials placed as a stack and in juxtaposition, at least one or twomaterials partly constituting this combination being bonded to the twoelements to be joined together.

For all these versions, when the strip also comprises the adhesivematerial, the latter may be placed so as to be stacked with and/or injuxtaposition with the damping material or materials. The nondampingadhesive material is, for example, a polyurethane mastic having aYoung's modulus E′ of 21 MPa and a loss factor tan δ of 0.2.

According to one feature, the damping material or materials, together orwith the adhesive material, are separated by an air space.

Advantageously, the damping material or materials are chosen from thefollowing plastics: plasticized or unplasticized polyvinyl chloride;thermoplastic elastomers; one-component or two-component polyurethanespossibly modified by an elastomer, such as polyolefins, EPDM(ethylene-propylene-diene) or rubber, especially butyl rubber or nitrilerubber or else styrene-butadiene rubber; polyalkyl acrylate ormethacrylate copolymers; and epoxy resins.

According to a first version of the composition, the damping material isa one-component polyurethane that has an NCO percentage content ofbetween 0.5 and 2% and comprises:

-   -   at least one polyesterpolyol with a functionality of two        (preferably between 80 and 200 g), having an OH index iOH of        between 5 and 10, a glass transition temperature T_(g) of        −50° C. or below and a softening point between 50 and 80° C.;    -   at least one polyesterpolyol with a functionality of two        (preferably between 120 g and 220 g), having an index iOH        between 50 and 100 and a glass transition temperature T_(g) of        −50° C. or below;    -   at least one isocyanate with a functionality of between 2.1 and        2.7 of the diphenylmethane diisocyanate (MDI) type and having an        NCO percentage content of between 11 and 33% (preferably between        180 and 220 g);    -   at least one catalyst (preferably between 0.5 and 3 g);    -   optionally, a filler of the molecular sieve type (preferably        between 20 and 60 g); and    -   optionally, at least one filler of the chalk, kaolin, talc,        alumina, carbon black or graphite type (preferably between 5 and        60 g).

With such a composition, the strip formed from the single material has,at 20° C., with a reference cross section of 15 mm in width and 3 mm inthickness, an equivalent real stiffness per unit length of 400 MPa andan equivalent loss factor of 0.3.

According to yet another version of the composition, the dampingmaterial is a polyurethane prepolymer that has an NCO percentage contentof between 0.5 and 2%, the material comprising:

-   -   at least one polyetherpolyol with a functionality of two, having        an index iOH of between 25 and 35, a glass transition        temperature T_(g) below −50° C. and a molecular mass between        3500 and 4500;    -   at least one polyetherpolyol with a functionality of between 2.3        and 4, having an index iOH between 25 and 800 and a glass        transition temperature T_(g) below −50° C.;    -   at least one polyesterpolyol with a functionality of two, having        an index iOH between 20 and 40 and a glass transition,        temperature T_(g) between −40 and −20° C.;    -   at least one polyesterpolyol with a functionality of two, having        an index iOH between 30 and 90, a glass transition temperature        T_(g) between 0 and 30° C. and a softening point between 50 and        70° C.;    -   at least one isocyanate with a functionality of between 2.1 and        2.7 of the diphenylmethane diisocyanate (MDI) type and an NCO        percentage content between 11 and 33%;    -   at least one catalyst;    -   optionally, a filler of the molecular sieve type; and        optionally, a filler of the chalk, kaolin, talc, alumina, carbon        black or graphite type.

The strip has, at 20° C., with such a composition, with a referencecross section of 15 mm in width and 3 mm in thickness, an equivalentreal stiffness per unit length of 120 MPa and an equivalent loss factorof 0.75.

According to yet another feature of the invention, the strip is appliedto at least one of the elements by a process of extrusion, and/or ofencapsulation, and/or of transfer from a molding, and/or of injectionmolding.

Finally, the strip may have a uniform or non-uniform cross section overall or part of its length.

The strip is therefore inserted between two elements that may be of themetal-metal, glass-glass, metal-plastic, glass-plastic orplastic-plastic type.

As an example, the strip-may be inserted between a glass substrate and ametal element so as to be used to attach the substrate to the metalelement. In particular in its use in automobile glazing, when it isplaced between the glazing and the bodywork, the strip provides theglazing with improved acoustic damping properties, and especially withrespect to solid-borne noise, that is to say for low frequencies ofaround 50 to 300 Hz. The inventors have also been able to show that theproperties could even be achieved for noise in the 300 to 1000 Hz range,known as dirty noise, in particular for laminated glazing assemblies.

Finally, the inventors have demonstrated that this strip may alsoprovide acoustic damping of aerodynamic noise, that is to say forfrequencies above 1000 Hz, when, however, the glazing is moreparticularly monolithic, that is to say formed from a single sheet ofglass.

The strip of the invention may therefore be used for glazing,particularly automobile glazing. The glazing may be formed from amonolithic glass, a laminated glass or what is called an “acoustic”laminated glass, i.e. one incorporating a plastic film having acousticproperties.

Finally, the invention defines a method of evaluating the acousticdamping properties of a strip designed to be inserted between twoelements formed from at least one damping material i, characterized inthat it consists in evaluating the equivalent real stiffness per unitlength K′_(eq) of the strip and the equivalent loss factor tan δ_(eq),the strip having acoustic damping properties when the equivalent realstiffness per unit length is equal to at least 25 MPa and the equivalentloss factor is equal to at least 0.25.

The evaluation of the equivalent real stiffness per unit length K′_(eq)of the strip and of the equivalent loss factor tan δ_(eq) is carried outusing a viscoanalyzer, as explained above.

Other advantages and features of the invention will become apparent inthe rest of the description given in conjunction with the appendeddrawings in which:

FIGS. 1 a to 1 c show partial sectional views of two elements joinedtogether by means of a strip in three versions of a first embodiment ofa strip of the invention;

FIGS. 2 a to 2 d illustrate partial sectional views of two elementsjoined together by means of a strip according to versions of a secondembodiment of the strip, the strip being formed from a stack ofmaterials;

FIGS. 3 a to 3 d illustrate partial sectional views of two elementsjoined together by means of a strip according to versions of a secondembodiment of the strip, the strip being formed from a juxtaposition ofmaterials;

FIGS. 4 a to 4 d illustrate partial sectional views of two elementsjoined together by means of a strip according to versions of a secondembodiment of the strip, the strip being formed from a combination ofone or more stacks and one or more juxtapositions of materials;

FIG. 5 shows schematically the steps for joining two elements togetherby means of the strip according to the first embodiment;

FIG. 6 shows a side view of one version of a strip bonded to one of theelements to be joined together;

FIG. 7 shows schematically the steps for joining two elements togetherby means of the strip according to the second embodiment;

FIGS. 8 a to 8 f illustrate, in cross section or in side view, otherversions of the strip bonded to one of the elements to be joinedtogether;

FIG. 9 shows schematically the steps for joining two elements togetherby means of this strip according to the version in FIG. 8 a;

FIGS. 10 a and 10 b illustrate two versions of the coextrusion of twodamping materials bonded to one of the elements to be joined together;

FIGS. 11 a and 11 b show schematically the steps for joining twoelements together by means of the strip according to the two versions ofthe type in FIG. 4 d;

FIG. 12 shows the modal damping in the first flexural mode obtained on aglass substrate provided with the strip, as values of the equivalentreal stiffness per unit length K′_(eq) plotted against values of theequivalent loss factor tan δ_(eq); and

FIG. 13 shows curves of the measured noise as a function of the enginespeed of an automobile for three types of strip.

These figures are schematic and the relative proportions of the variousquantities, especially the thicknesses and widths, between the variouselements of the invention have not been drawn to scale so as to makethem easier to examine.

FIG. 1 a is a partial sectional view of a glazing assembly 1 joined to acarrier element 2, such as the bodywork of an automobile. The glazingassembly, formed from at least one glass substrate, is attached to thebodywork by means of a strip 3 with acoustic damping properties.

Consequently, the strip 3, joined to and inserted between two elements 1and 2 that are, for example, the bodywork and the glazing respectively,fulfillls, apart from its vibration damping function according to theinvention, the function of a device for bonding the two elements, whileproviding a sealing function in order to protect the passengercompartment of the vehicle from exposure to the external environment,such as exposure to dust, moisture, water. However, in anotherapplication, the strip could be inserted between the two elements onlyto fulfilll just its damping function, without fulfillling a function ofbonding the two elements together. For example, the strip may beattached to a first element, such as a door frame of a room inside abuilding and may be joined to a second element, such as the door when itis closed; the strip, being stressed by the surfaces of the door and ofthe frame sufficiently to absorb the exciting energy of the frame,reduces the acoustic radiation inside the volume closed by said door.

The construction of the strip 3 will be described below. The strip maybe embellished with functional forms that are not specifically acoustic,such as with sealing lips or with a trim.

The acoustic damping properties of the strip are defined by theequivalent stiffness per unit length and the loss factor parameters.

The strip may be formed from a single material or else from a pluralityof materials, and in the latter case it is necessary to take intoaccount the stiffness per unit length of each material. This is why theterm “equivalent stiffness per unit length”, denoted by K*_(eq), isused, which term therefore corresponds to the equivalent stiffness forthe entire strip and the word “linear” being used to indicate that itrelates to 1 m of strip.

The equivalent stiffness per unit length K*_(eq) is known to be acomplex number written as K*_(eq)=K′_(eq)+j K″_(eq) with a real partK′_(eq), called in the description the equivalent real stiffness perunit length, and an imaginary part K″_(eq) that corresponds to the lossfactor, that is to say to the conversion of the deformation energy ofthe strip into thermal energy throughout the entire strip.

K*_(eq) may be written according to the following formula, because thestrip may comprise several materials: $\begin{matrix}{\left\lbrack K_{eq}^{*} \right\rbrack^{\alpha} = {\sum\left\lbrack K_{i}^{*} \right\rbrack^{\alpha}}} & (1)\end{matrix}$where:

K*_(i) is the complex stiffness per unit length of each constituentmaterial i of the strip;

α=−1 for a stack of several materials i arranged in series, that is tosay in an arrangement called a stack in the rest of the description;

α=1 for a juxtaposition of several materials i in parallel, that is tosay in an arrangement called a juxtaposition in the rest of thedescription.

In the case of a combination of a stack and a juxtaposition, theequivalent stiffness per unit length of the stack and of thejuxtaposition will be calculated and the strip will then be normalizedto just a stack or to just a juxtaposition such that α=−1 or α=1,respectively.

This gives, for example for two materials in series:1/K*eq=1/K*1+1/K*2i.e. 1/(K′eq+jK″eq)=1/(K′1+jK′1)+1/(K′2+jK″2)hence:K′eq=[K′1² K′2+K″1² K′2+K′1K′2² +K′1K″2²]/[(K′1+K′2)²+(K″1+K″2)²]andK″eq=[K′1² K″2+K″ ² K″2+K″1K′2² +K″1K″2²]/[(K′1+K′2)²+(K″1+K″2)²].For two materials in parallel, then:K′ _(eq) =K′1_(eq) +K′2_(eq) and K″ _(eq) =K″1_(eq) +K″2_(eq).

Examples of stacked and/or juxtaposed arrangements of a number ofmaterials i will be described below with reference to FIGS. 1 a to 1 c,2 a to 2 d, 3 a to 3 d and 4 a to 4 d.

Moreover, the stiffness per unit length depends on the rigidity of theconstituent material or materials of the strip, but also on thedimensional quantities of the cross section of each constituent materialof the strip.

Thus, the stiffness per unit length K*_(i) for a given material inequation (1), being normalized to a strip length of 1 m and to arectangular cross section of width L_(i) and thickness e_(i), and basedon the principle that the strip is subjected to tensile/compressivestresses that are uniform over the width (the shear being ignored), maybe written as: $\begin{matrix}{K_{i}^{*} = {E_{i}^{*} \times \frac{L_{i}}{e_{i}}}} & (2)\end{matrix}$where E*_(i) is the complex Young's modulus of the constituent materiali of the strip.

By separating equation (2) into the real and imaginary parts, it may bealso written as:$K_{i}^{*} = {{K_{i}^{\prime} + {j\quad K_{i}^{''}}} = {{E_{i}^{\prime} \times \frac{L_{i}}{e_{i}}} + {j\quad E_{i}^{''} \times \frac{L_{i}}{e_{i}}}}}$where E′_(i) is the real part of the complex Young's modulus and calledjust Young's modulus in the description; and E″_(i) is the imaginarypart of the complex Young's modulus.

The reader is reminded that, in the invention, one of the parameterscharacterizing the acoustic properties of the strip is the equivalentreal stiffness per unit length K′_(eq), i.e. the real part of thecomplex number K*_(eq). As explained above, K′_(eq) may be estimated bycalculation after having measured the Young's modulus E′_(i) of eachmaterial using a viscoanalyzer. K′_(eq) may be measured using aviscoanalyzer in order to check the calculations.

These calculations are appropriate, however, when the shape of the stripis rectangular. For any other shape, this quantity will in fact bemeasured using the viscoanalyzer.

The selection of materials to be used so as to form the strip when thesematerials are not of simple rectangular shape will be made on the basisof approximation calculations, by approximating the actual cross sectionof each material to a rectangular cross section for which the strip issubjected to the tensile-compressive forces. If the calculations arefavorable to this selection of materials, as they satisfy the claimedcriteria that will be presented below, these calculations will have tobe checked by measurement using the viscoanalyzer.

According to the invention, in order for the strip 3 to fulfilll itsacoustic damping function, it must have an equivalent real stiffness perunit length K′_(eq) equal to at least 25 MPa. Preferably, the equivalentreal stiffness per unit length K′_(eq) is between 30 and 250 MPa.

In addition, as was mentioned above, involved in the acoustic dampingproperties of the strip is the equivalent loss factor (or the tangent ofthe equivalent loss angle) tan δ_(eq) that is defined by the equation:$\begin{matrix}{{\tan\quad\delta_{eq}} = \frac{K_{eq}^{''}}{K_{eq}^{\prime}}} & (3)\end{matrix}$where K′_(eq) is the equivalent real stiffness per unit length (the realpart of K*_(eq)) for the entire strip and K″_(eq) is the loss modulus(imaginary part of K*_(eq)).

In a manner similar to that of estimating the equivalent real stiffnessper unit length, the loss factor will be estimated by calculation usingequation (3), equations (1) and (2) serving to calculate K′_(eq) andK″_(eq), K′_(eq) and K″_(eq) being estimated by calculation using themeasurement by the viscoanalyzer of the real part and of the imaginarypart of the complex Young's modulus of each constituent material of thestrip, respectively. The measurement from the entire strip using theviscoanalyzer will be used to confirm the calculations, particularlywhen selecting materials of any nonrectangular cross section.

In all cases, to ensure that the strip meets the claimed criterion thatwill be presented below regarding this loss factor, a measurement of theequivalent real stiffness per unit length by the viscoanalyzer and acalculation of the loss factor will be made.

According to the invention, the strip 3 exhibits acoustic dampingproperties when the equivalent loss factor tan δ_(eq) of the strip isequal to at least 0.25.

The equivalent loss factor and the equivalent real stiffness per unitlength depend not only on the chemical nature of the material ormaterials of the strip but also on the geometry given to the crosssection of the strip. In addition, when a strip meets the claimedcriteria according to the invention regarding the equivalent loss factorand the equivalent stiffness per unit length, it is possible to optimizethese parameters by modifying them so as to further enhance the acousticperformance.

These parameters are modified by changing the dimensions of the crosssection of the strip. For example, if the strip is formed from a singlematerial and has a rectangular cross section, its equivalent realstiffness per unit length is then increased by reducing the thickness eof the strip and by increasing its width L.

The strip 3 may be formed structurally in various ways.

According to a first embodiment illustrated in FIGS. 1 a to 1 c, thestrip 3 is formed from at least one damping material 4 that fulfilllsthe acoustic damping function and also the function of bonding the twoelements together and optionally the sealing function, depending on thetype of use for which the strip is intended. In the example in questionof glazing for an automobile, the strip preferably also fulfillls thesealing function. This strip configuration comprising one or moredamping materials that also fulfilll an adhesive function for bondingthe two elements together will be called in the rest of the descriptiona monolithic strip.

According to this first embodiment, a first version (FIG. 1 a) consistsin making the strip from a single material that meets the stipulatedcriteria as regards the equivalent loss factor and the equivalent realstiffness per unit length and that has the properties of adhesion to thetwo elements 1 and 2, and if necessary sealing properties.

A second version of the first embodiment consists in making the strip 3from two damping materials 4 a and 4 b that meet the criteria of theinvention. These materials, one of which may be relatively more dampingor less damping than the other, result, when they are combined, in anequivalent real stiffness per unit length and an equivalent loss factorthat meet the damping criteria. They are placed as layers one on top ofthe other (FIG. 1 b) or are juxtaposed one beside the other (FIG. 1 c)and optionally separated by an air gap (not illustrated). Both materialsexhibit adhesion properties with respect to at least one of the twoelements to which they are joined.

It is also possible to envision more than two damping materials taken incombination as a juxtaposition or as a stack (not illustrated).

Examples of materials that can be used for a monolithic strip will bementioned later in the description.

According to a second embodiment illustrated in FIGS. 2 a to 2 d, 3 a to3 d and 4 a to 4 d, the strip 3 is formed from at least one dampingmaterial 4 and from a nondamping adhesive material 5. The material 4provides the acoustic damping function and is bonded to at least one ofthe two elements 1 and 2 to be joined together, whereas the adhesivematerial 5 provides the function of bonding the two elements 1 and 2together, being bonded to at least one of the two elements 1 and 2. Thematerials 4 and 5 are chemically compatible in order to guarantee, ifnecessary, depending on the embodiment, their mutual adhesion. Thematerials 4 and 5 may exhibit sealing properties depending on the use ofthe strip.

In this second embodiment, the nondamping adhesive material 5 servesmerely to bond the two elements 1 and 2 and also has sealing properties.By itself it has no acoustic damping property. However, it is necessaryfor it to have an appropriate thickness and width, since it has aYoung's modulus E_(i)′ and a loss factor tan δ that have an influence onthe equivalent real stiffness per unit length and the equivalent lossfactor of the entire strip 3 and therefore on the acoustic dampingproperties of the entire strip 3.

In this second embodiment, the arrangement of the materials between thetwo elements may vary.

It may be of the stacked type (FIGS. 2 a to 2 d), i.e. the materials arearranged in layers one on top of another, each of the materials at theends of the stack being bonded to one of the two elements 1 and 2 to bejoined together.

It may be of the juxtaposed type (FIGS. 3 a to 3 d), i.e. the materialsmay or may not be beside one another, each of the materials having twoopposed surfaces bonded to the two elements 1 and 2 to be joinedtogether, respectively.

A third type of version of the second embodiment is an arrangement inwhich a stack is combined with a juxtaposition (FIGS. 4 a to 4 d), atleast one or two materials partly constituting this combination beingbonded to the two elements 1 and 2 to be joined together.

FIG. 2 a to 2 d therefore illustrate different versions of a stackarrangement.

The stacks in FIGS. 2 a and 2 b consist of a material 4 with acousticdamping properties and of a nondamping material 5 for adhesion of thestrip to one of the elements. In FIG. 2 a, the material 4 is bonded tothe element 1—the glass substrate—and the adhesive material 5 adheresvia one of its faces 50 to the damping material 4 and adheres by itsopposite face 51 to the element 2—the bodywork, whereas in FIG. 2 b thematerials 4 and 5 are bonded to the bodywork and to the glass substrate,respectively. The layers of material have the same width L1 and each hasa thickness e1, e2 that is tailored to the nature of the material, andtherefore to the loss factor of each material so as to optimize theequivalent real stiffness per unit length and/or the equivalent lossfactor of the strip.

FIGS. 2 c and 2 d correspond to a stack of three materials—two materials40 and 41 constitute the damping material 4 and the third materialconstitutes the adhesive material 5. The layers of material are ofidentical width in the case of FIG. 2 c, but of different width in thecase of FIG. 2 d, the thickness of each of the layers being designed tooptimize the equivalent real stiffness per unit length and/or theequivalent loss factor of the strip 3.

FIGS. 3 a to 3 d illustrate different versions of the juxtaposedarrangement.

In FIG. 3 a, the juxtaposition of two materials consists of a dampingmaterial 4 placed beside an adhesive material 5, both having the samethickness and bonded by two of their opposed faces, 50 and 51 in thecase of the adhesive material, to the two elements 1 and 2, namely theglass substrate and the bodywork. Their widths L1 and L2 are defined soas to optimize the calculation of the equivalent real stiffness per unitlength and/or the equivalent loss factor.

FIG. 3 b shows the materials 4 and 5 in FIG. 3 a reversed, thenondamping adhesive material being placed on the side facing thepassenger compartment of the vehicle.

FIG. 3 c is a repeat of FIG. 3 a, except that the materials are notbeside each other but separated by an air gap 6.

FIG. 3 d is representative of a juxtaposition of three materials besideone another—a nondamping adhesive material 5 sandwiched between twodamping materials 42 and 43 that constitute the damping material 4. Thematerials 42 and 43 may or may not be different.

Depending on the thickness of the various materials placed injuxtaposition, the width of each damping material 4 (and therefore also42 and 43) and of each adhesive material 5 is designed to ensure thatthe equivalent real stiffness per unit length and the equivalent lossfactor of the combination of materials, and therefore of the strip 3,are sufficient for the desired acoustic damping.

FIGS. 4 a to 4 d show a combination of stacked and juxtaposedarrangements, at least the adhesive material being bonded via twoopposed faces to the elements 1 and 2 to be joined together.

FIG. 4 a is a juxtaposition of the adhesive material 5 and the dampingmaterial 4, the latter being formed from a stack of different materials44 and 45, one being more damping than the other.

FIG. 4 b is a repeat of FIG. 4 a, except that the adhesive material 5and the damping material 4 (44, 45) are separated by an air gap 6.

FIG. 4 c illustrates a juxtaposition of several materials beside oneanother, the adhesive material 5 being sandwiched between dampingmaterials 4 that consist of two stacks of at least two differentmaterials 46, 47, it being possible for the stacks to differ from eachother.

FIG. 4 d illustrates a juxtaposition of three materials beside oneanother—the adhesive material 5 and two damping materials 4 that may ormay not be different. The adhesive material 5 is sandwiched between thetwo damping materials 4 and has one of its faces, 51, that extends overthe width L of the strip and is bonded to one of the elements 2 so thatthe materials 4 are stacked with a thickness e1 on a thickness e2 of thematerial 5. The opposite face 50 of the adhesive material 5 is bonded tothe other element 1 and has a width L2, whereas the materials 4 areplaced against said element 1 with widths of L1 and L3.

In the second embodiment, in which the nondamping adhesive material 5 isdifferent from the damping material 4, the adhesive material 5, which isalso used to provide the sealing function, is for example a polyurethanemastic such as GURIT BETASEAL 1720 sold by Dow Automotive. In theexample given, it seals the glazing with respect to the bodywork and isimpermeable to gases, dust, water vapor, liquid water and solvents.

The inventors have identified several plastics that can provide thedamping properties required of the damping material 4 of the firstembodiment or of the second embodiment in any of the versions referenced40 to 47.

For example, mention may be made of:

-   -   plasticized or unplasticized polyvinyl chloride;    -   thermoplastic elastomers;    -   one-component or two-component polyurethanes, possibly modified        by an elastomer, such as polyolefins, EPDM        (ethylene-propylene-diene) or rubber, especially butyl rubber or        nitrile rubber or styrene-butadiene rubber;    -   polyalkyl acrylate or methacrylate copolymers; and    -   epoxy resins.

The compositions mentioned above may furthermore contain organic ormineral fillers, such as talc, silica, calcium carbonate, kaolin,alumina, molecular sieve, carbon black, graphite or pyrogenic silica,and metal fillers such as zinc oxide, titanium oxide, alumina ormagnetite. The filler content may vary between 0 and 50% by weight ofthe final composition.

As regards thermoplastic elastomers (TPE), these consist of blends ofpolymers or of block copolymers exhibiting a thermoplastic phase and anelastomer phase, optionally these being chemically bonded together inthe case of copolymers.

As regards polyurethanes, thermoplastic urethanes (TPU), that exist forexample in the form of a nonreactive polymer obtained from severalpolyol sources, at least one form of which is a block havingthermoplastic properties and at least one other form of which is a blockhaving elastic properties, may be considered.

It is also possible to select a polyurethane-based material with a widevariety of reactive compositions of the one-component or two-componenttype. As an example, mentioned may especially be made of one-componentcompositions based on a polyurethane prepolymer with a polyester,polyether, polycaprolactone, polyolefin or polysiloxane backbone. Theadvantage of a siloxane-terminated prepolymer is that it ismoisture-curable and does not foam. These polyurethane compositions maybe modified by an elastomer, especially by a nitrile, SBR or butylrubber, or by a thermoplastic elastomer or else by a non-crosslinkablepolymer having a certain flexibility, such as polyolefins or plasticizedPVC.

Among the moisture-crosslinkable and/or thermally crosslinkableone-component polyurethane prepolymer compositions are those obtained byreaction between polyols and polymeric or nonpolymeric diisocyanates.

The polyols of the compositions may be polyetherpolyols, of thepolyethylene, propylene oxide or polytetramethylene oxide type, apolycarbonate polyol or polybutadiene polyol or polyesterpolyols, thesebeing amorphous or crystalline, aromatic or aliphatic, and based onfatty acid dimers, aromatic or aliphatic diacids, castor oil or chainextenders of the 1,3- or 1,4-butanediol, diisopropyl glycol,2,2-dimethyl-1,3-propanediol, hexanediol or carbitol type. The molecularmass of these polyols will be defined by their hydroxyl index (iOH)defined in the ASTM E 222-94 standard as the number of milligrams ofpotassium hydroxide equivalent to the hydroxyl content of 1 gram ofpolyol. The NOH range used is between 5 and 1500. The functionality ofthese polyols will be between 2 and 6.

The isocyanates may be aromatic or aliphatic, among which arediphenyl-methane diisocyanates (MDI), toluene diisocyanates (TDI),isophorone diisocyanates (IPDI) and hexane diisocyanate (HDI). Thenature of the isocyanates is also defined by their NCO percentagecontent which, in the ASTM D 5155-96 standard, is defined as theproportion by weight of isocyanate (NCO) functional groups present inthe product. The functionality of the products is between 2 and 2.7.

The catalysts needed for the reaction between the polyols and theisocyanates may be tin catalysts such as dibutyltin dilaurate (DBTDL) ortin octoate. It is also possible to use bismuth catalysts or catalystsbased on morpholines, such as dimorpholinodiethyl ether (DMDEE).

To prevent the selected prepolymer from foaming, it is possible to addan antifoam additive, which is a compound based on bisoxazolidines.Finally, various plasticizers may also be advantageously added to theprepolymer selected.

In general, the strip 3 is applied between the elements 1 and 2 in thefollowing manner (FIG. 5): the strip 3 is deposited on the element 1 byan application technique that we will expand upon in the rest of thedescription. Depending on the chemical nature of the free surface of thestrip to be joined to the element 2, this surface is eitherconventionally bonded, as it has bonding properties at room temperature,or else this free surface is activated using an energy source 7 of theinfrared, ultraviolet, high-frequency, microwave or induction type, andwhen the surface reaches a suitable temperature, the strip joined to thefirst element 1, such as the substrate, is pressed against the secondelement 2, such as the bodywork, in order to bond them together. Theamount of energy and the thickness of the activated material ormaterials are gaged in order to obtain the final width and thicknessthat are desired between the two elements 1 and 2.

The strip 3 may be applied against the first element in various ways.The technique employed may depend on the nature of the material ormaterials and on the arrangement—stacked and/or juxtaposed—of thematerials.

At least four techniques for depositing the gaged strip may be used,separately or in combination: extrusion, overmolding (encapsulation) andtransfer from a molding. As regards the transfer process, reference maybe made for further details to French patent application FR 01/15039.

The extrusion technique ensures that the strip has a constant geometry.Advantageously, the shape given to the strip may make it easier for itto be bonded to the element to which it is joined in order to guaranteethe desired geometry. The damping materials used must have viscositiesbetween 100 and 500 Pa·s at 80° C., the materials setting below 50° C.The materials will therefore have a green strength and a thixotropy thatare sufficient to maintain their geometry after extrusion. Preferably,they will be of the one-component type and will ensure good bonding tothe first element being joined to it, such as the glass substrate in theexample cited.

In the second technique, the strip may be overmolded on one of theelements so as advantageously to give it any of the desired shapes andthus optimize the acoustic performance, while guaranteeing thedimensions of the strip at any point on the glazing, as it may benecessary for the width and the thickness of the strip not to be uniformover the entire perimeter of the element to which it is joined for therequirements of the acoustic performance (FIG. 6). The viscosity of thematerials used must not exceed a certain limit and the setting of atwo-component product must be rapid.

In the third technique, the strip may also be molded and transferred toone of the elements in order to preserve the advantages of the moldingand to reduce the mold production costs. This technique combines theadvantages of extrusion and overmolding, as it allows several layers ofmaterials of various shapes to be created, as illustrated in FIG. 2d. Asin the case of extrusion, a minimum green strength and a minimumviscosity of the materials are required for moisture-crosslinkingone-component materials. The setting time may be rapid if thermallycrosslinking one-component-type systems are employed. As regardstwo-component systems, these set rapidly.

Finally, an injection molding technique is also conceivable. In thiscase, the element to which the material has to be joined is placed in amold having a cavity corresponding to the shapes of the strip that it isdesired to produce and molding material formed by the damping materialis injected in the molten state into the mold.

Among the examples of techniques used, a distinction will be made belowbetween joining the two elements together according to the firstembodiment of the strip, that is to say as a monolithic strip, andaccording to the second embodiment, namely when the strip comprises atleast two materials 4 and 5 corresponding to the damping material and tothe nondamping adhesive material, respectively.

In the case of a monolithic strip 3, it is applied against the glasssubstrate 1 by selecting one of the four techniques.

As regards extrusion against the element 1, therefore with a singledamping material 4 that also provides the function of bonding to theelement, the inventors have developed a material A that meets thecriteria of the invention, the surface of which is activatable so as tobe bonded to the element 2. This is a moisture-crosslinkingone-component polyurethane having a single glass transition temperatureT_(g) and comprising:

-   -   at least one polyesterpolyol with a functionality of two        (preferably between 80 and 200 g), having an OH index iOH of        between 5 and 10, a glass transition temperature T_(g) of        −50° C. or below and a softening point between 50 and 80° C.;    -   at least one polyesterpolyol with a functionality of two        (preferably between 120 g and 220 g), having an index iOH        between 50 and 100 and a glass transition temperature T_(g) of        −50° C. or below;    -   at least one isocyanate with a functionality of between 2.1 and        2.7 of the diphenylmethane diisocyanate (MDI) type and having an        NCO percentage content of between 11 and 33% (preferably between        180 and 220 g);    -   at least one catalyst (preferably between 0.5 and 3 g);    -   optionally, a filler of the molecular sieve type (preferably        between 20 and 60 g); and    -   optionally, at least one filler of the chalk, kaolin, talc,        alumina, carbon black or graphite type (preferably between 5 and        60 g).

The NCO percentage content of this polyurethane prepolymer A is between0.5 and 2%.

For such a material A used to form a strip of rectangular cross sectionequal to the reference cross section L×e=15 mm×3 mm, the value of theYoung's modulus E′ measured at 120 Hz and at an ambient temperature of20° C. is 80 MPa. The equivalent loss factor, consisting of the lossfactor of the single material is then equal to 0.3 and the equivalentreal stiffness per unit length is equal to 400 MPa.

For the application of a strip 3 formed from at least two materials 4and 5 according to the second embodiment, it is possible to coextrudethe two materials onto the glass substrate 1. After this first step, thebonding is effected by heating the free surface of the strip and byapplying it against the bodywork (FIG. 7), or else by applying the freesurface directly against the bodywork, depending on the nature of thematerials.

Alternatively, it is possible to overmold or transfer after molding,onto the glass substrate, the damping material 4, giving it the desiredshape (FIGS. 8 a to 8 f). The adhesive material 5 is then deposited onthe free surface of the damping material 4 by extrusion (FIG. 9). It isthus possible to give the damping material a particular profile with,for example, rims 48 (FIGS. 8 a, 8 b, 8 c) that serve to guide theadhesive material and to define the thickness and/or the width of saidadhesive material during its deposition, or else, for example, withcentral projections 49 (FIGS. 8 d, 8 e, 8 f) that allow the thickness ofthe adhesive material to be gaged. For bonding, the surface of theadhesive material 5 deposited on the damping material 4 is, ifnecessary, heated and the strip is pressed against the bodywork (FIG.9).

If the strip 3 is formed from an adhesive material 5 and two dampingmaterials 40 and 41 of the stacked type, the two damping materials maybe coextruded onto the glass substrate 1 as illustrated by the twoversions in FIGS. 10 a and 10 b. The deposition of the adhesive material5 on the free surface of the damping material on the opposite side fromthe substrate and the bonding are then carried out as illustrated inFIG. 9.

FIGS. 11 a and 11 b show the steps of bonding the element 1 to theelement 2 by means of two respective versions of a strip of the typeillustrated in FIG. 4 d. The material 4 is firstly molded andtransferred to the element 1. It has a particular geometry, inparticular it is separated into two parts 400 and 401 so as to form areceiving channel 402 for housing the adhesive material 5 duringbonding. The adhesive material 5 has in the end two opposed faces bondedto the two elements 1 and 2, respectively.

One example of a strip, comprising at least one damping material 4 andat an adhesive material 5, is formed from a material B as dampingmaterial 4 and from an adhesive mastic 5, such as a nondampingpolyurethane mastic. Each of the materials has a rectangular crosssection 15 mm in width and 3 mm in thickness, representing a total crosssection equal to the reference cross section in the case of the strip 15mm in width and 6 mm in thickness.

The material B of composition developed by the inventors is of themoisture-crosslinking one-component polyurethane type with a singleglass transition temperature and comprising:

-   -   at least one polyesterpolyol with a functionality of two        (preferably between 350 and 450 g), having an OH number between        20 and 40 and a glass transition temperature T_(g) of between        −40 and −20° C.;    -   at least one polyesterpolyol with a functionality of two, having        an OH number between 30 and 90 (preferably between 35 and 250        g), a glass transition temperature T_(g) between 0 and 30° C.        and a softening point between 50 and 70° C.;    -   at least one isocyanate having a functionality between 2.1 and        2.7 of the diphenylmethane diisocyanate (MDI) type and an NCO        percentage content of between 11 and 33% (preferably between 150        and 230 g);    -   at least one catalyst (preferably between 0.5 and 3 g);    -   optionally, a filler of the molecular sieve type (preferably        between 20 and 80 g); and    -   optionally, at least one filler of the chalk, kaolin, talc,        alumina, carbon black or graphite type (preferably between 5 and        60 g).

The NCO percentage content of this polyurethane prepolymer B is between0.5 and 2%.

The Young's modulus and loss factor values of the damping material B atan ambient temperature of 20° C. are the following: E′=35 MPa and tanδ=1.4.

The Young's modulus and loss factor values of the nondamping adhesivematerial 5 made of a polyurethane mastic, at 120 Hz and at an ambienttemperature of 20° C., are the following: E′=21 MPa and tan δ=0.2.

The equivalent real stiffness per unit length and the equivalent lossfactor values are equal to 70 MPa and 0.95, respectively.

The inventors have also developed another damping material C that hasadhesive properties, particularly with an adhesive strength at lowtemperature (between −60 and −10° C.). This material, unlike thematerials A and B, has two glass transition temperatures. It is apolyurethane prepolymer comprising:

-   -   at least one polyetherpolyol with a functionality of two, having        an index iOH of between 25 and 35, a glass transition        temperature T_(g) below −50° C. and a molecular mass between        3500 and 4500;    -   at least one polyetherpolyol with a functionality of between 2.3        and 4, having an index iOH between 25 and 800 and a glass        transition temperature T_(g) below −50° C.;    -   at least one polyesterpolyol with a functionality of two, having        an index iOH between 20 and 40 and a glass transition        temperature T_(g) between 40 and −20° C.;    -   at least one polyesterpolyol with a functionality of two, having        an index iOH between 30 and 90, a glass transition temperature        T_(g) between 0 and 30° C. and a softening point between 50 and        70° C.;    -   at least one isocyanate with a functionality of between 2.1 and        2.7 of the diphenylmethane diisocyanate (MDI) type and an NCO        percentage content between 11 and 33%;    -   at least one catalyst;    -   optionally, a filler of the molecular sieve type; and    -   optionally, a filler of the chalk, kaolin, talc, alumina, carbon        black or graphite type.

The NCO percentage content of this polyurethane prepolymer is between0.5 and 2%.

In particular, we may describe as compound in accordance withcomposition C above, the NCO % content being between 1.8 and 2.2%, andcomprising:

-   -   between 180 and 220 g of a polyetherpolyol with a functionality        of two, having an index iOH between 25 and 35, a glass        transition temperature T_(g) below −50° C. and a molecular mass        between 3500 and 4500;    -   between 75 and 115 g of an isocyanate of the MDI type having an        NCO % content equal to 11.9%;    -   between 5 and 30 g of carbon black;    -   between 0.5 and 3 g of catalyst;    -   between 10 and 30 g of pyrogenic silica;    -   between 135 and 180 g of a liquid and amorphous polyesterpolyol        A with an index iOH between 27 and 34, a molecular mass of 3500,        a functionality of two and a glass transition temperature T_(g)        of −30° C.;    -   between 35 and 85 g of a liquid and amorphous polyesterpolyol B        with an index iOH between 27 and 34, a molecular mass of 3500, a        functionality of two and a glass transition temperature T_(g) of        +20° C., respectively;    -   between 55 and 110 g of an MDI-type isocyanate, with an NCO %        content of 11.9%; and    -   between 20 and 80 g of molecular sieve.

For such a material C used to form a strip of rectangular cross sectionequal to the reference cross section L×e=15 mm×3 mm, the value of theYoung's modulus E′ measured at 120 Hz and 20° C. is 22 MPa. Theequivalent loss factor, which consists of the loss factor of the singlematerial, is equal to tan δ=0.75 and the equivalent real stiffness perunit length is equal to 120 MPa.

This material C having two glass transition temperatures may also verywell be used at low temperature, as it exhibits not only acousticdamping properties but also adhesive strength. In fact, at −40° C., theloss factor is equal to 0.38 and the value of Young's modulus is 900MPa, the inventors defining the adhesive strength property, that is tosay when there is no risk of adhesive failure between the material andthe element to which it is joined, such that the rigidity E′ of thematerial is less than 2000 MPa for a frequency between 50 and 500 Hz.

The inventors have therefore succeeded in selecting damping materialcompositions that meet the equivalent real stiffness per unit length andequivalent loss factor criteria stipulated by the invention. To checkwhether the material or materials to be used in a strip with acousticdamping properties and the shape of the cross section of this or thesematerials do meet the criteria provided by the invention, the inventorshave established a method of evaluation.

When dealing with rectangular cross sections of materials, it isnecessary:

-   -   to measure the Young's modulus E_(i)′ and the loss modulus        E_(i)″ of the material or materials to be used for the strip;    -   to evaluate the equivalent real stiffness per unit length        K′_(eq) and the equivalent loss factor tan δ_(eq) from the        abovementioned equations (1), (2) and (3); and    -   finally, to compare these K′_(eq) and tan δ_(eq) values of the        strip with the reference values, 25 MPa and 0.25 respectively,        above which the acoustic properties are obtained.

It will be possible to optimize the values of these parameters, andtherefore to achieve better noise attenuation, by varying thethicknesses and widths of the materials.

The Young's modulus E_(i)′ and loss modulus E_(i)″ values of eachmaterial are measured using a viscoanalyzer like the one sold under thebrand name METRAVIB under the measurement conditions given below:

-   -   sinusoidal stressing;    -   material specimen formed from a rectangular parallelepiped with        dimensions that lie within the ranges defined by the        manufacturer of the visco-analyzer, for example:        -   thickness e=3 mm        -   width L=5 mm        -   height=10 mm    -   dynamic amplitude: ±5×10 ⁻⁶ m around the rest position,    -   frequency range: 5 to 400 Hz    -   temperature range: −60 to +60° C.

The viscoanalyzer allows a material specimen to be subjected todeformation stresses under precise temperature and frequency conditions,and in this way to obtain and treat all the Theological, quantities thatcharacterize the material.

The raw data—force, displacement and phase shift measurements as afunction of frequency at various temperatures—is used in particular toestablish the Young's modulus E_(i)′ and the loss modulus E_(i)″ of thematerial.

To confirm the method of evaluation, described above, for seekingmaterials and dimensions, and in all cases to ensure that a strip hasthe features claimed by the invention, the viscoanalyzer is used to makedirect measurements of the equivalent real stiffness and the equivalentloss modulus of a strip specimen of cross section identical to that ofthe strip and of length L. The following then have to be calculated:

-   -   the ratio of the measured equivalent real stiffness to the        length L in order to obtain the equivalent real stiffness per        unit length K′_(eq) of the strip: K′_(eq)=k′_(eq)/L; and    -   the ratio of the measured equivalent loss factor to the measured        equivalent real stiffness in order to obtain the equivalent loss        factor tan δ_(eq) of the strip:        $\frac{k_{eq}^{''}}{k_{eq}^{\prime}}.$

Finally, the inventors have chosen to illustrate the acousticperformance of the strip 3 by plotting the equivalent real stiffness perunit length K′_(eq) as a function of the equivalent loss factor tanδ_(eq) in the graph shown in FIG. 12. The values of the equivalent lossfactor are plotted on the x-axis and the values of the equivalent realstiffness per unit length are plotted on the y-axis. On the basis ofthese values, the graph indicates the modal damping in the firstflexural mode measured on a glass substrate (800 mm by 500 mm and 4 mmin thickness) bonded to a bed by means of the strip placed around theperiphery and on one face of the substrate, it being possible for theequivalent loss factor tan δ_(eq) to be between 0.15 and 1, and for theequivalent real stiffness per unit length not to exceed 400 MPa. It maybe noted that the values of the gains given for tan δ_(eq)=1 may beextrapolated to tan δ_(eq)>1 for the same values of the equivalentstiffness.

The modal damping is expressed on a scale of 0 to 30%. The greater thedamping, the higher the acoustic gain in dB.

The modal damping in the first flexural mode is defined as follows. Themodal damping is deduced from measurements of the mechanical impedance Z(modulus of the frequency response function giving the vibration speednormal to the glass substrate at one point as a function of the pointload applied at this same point in the direction normal to saidsubstrate) made using an impact hammer and an accelerometer at thecenter of the substrate.

The frequency of the first flexural mode corresponds to that frequencybelow 120 Hz for which the mechanical impedance is a maximum. It isdenoted by f1. The value of the mechanical impedance of the frequency f1is denoted by Zmax.

The bandwidth at mid-height corresponds to the width of the frequencyrange around f1 for which Z>Zmax/√{square root over (2)}. It is denotedby Δf.

The modal damping of the first flexural mode corresponds to the ratioΔf/f1.

The graph shows from the values that the modal damping and therefore theacoustic performance (gain in dB) are variables for a given loss factorand different equivalent stiffnesses, or vice versa.

Thus, it is possible to obtain a modal damping close to 30% for anequivalent real stiffness per unit length of 100 MPa and a loss factorbetween 0.5 and 1, whereas the damping does not exceed 5% if the lossfactor is only 0.3 for the same real stiffness per unit length of 100MPa.

It may also be seen that for a loss factor of 0.8 for example, theoptimum equivalent real stiffness per unit length will be around 100 MPaand that increasing the equivalent real stiffness per unit length willonly decrease the modal damping that can be obtained.

This graph demonstrates that the use of the material A, as explainedabove for a monolithic strip and having an equivalent real stiffness perunit length of 400 MPa and an equivalent loss factor of 0.3, generatesmodal damping of between 5 and 10%.

The use of the material B combined with a nondamping polyurethane masticfor the strip taken as the above example in the second embodiment, thathas an equivalent real stiffness per unit length of 70 MPa and anequivalent loss factor of 0.95, generates modal damping of more than20%.

Moreover, FIG. 13 shows three comparative curves of the noise measuredinside an automobile as a function of the engine speed for three typesof strip.

Curve C1 corresponds to a standard laminated glazing assembly equippedwith a standard strip made from nondamping polyurethane mastic with areference cross section of 9 mm by 6 mm.

Curve C2 corresponds to a standard glazing assembly equipped with amonolithic strip according to the invention formed from the dampingmaterial 4 of composition A with a reference cross section of 15 mm by 3mm.

Curve C3 corresponds to a standard glazing assembly equipped with astrip according to the invention formed from the damping material 4 ofcomposition B and from the nondamping adhesive material 5 made of apolyurethane mastic with a reference cross section of 15 mm by 6 mm.

The term “standard laminated glazing assembly” is understood to mean onecomprising two 2.1 mm thick sheets of glass and a 0.76 mm thickinterlayer film of polyvinyl butyral.

The table below gives the values of the equivalent real stiffness perunit length and the equivalent loss factor for the three types of strip.Equivalent real stiffness per unit Type of strip; curve lengthEquivalent loss (reference cross section) (K′_(eq)) in MPa factor(tanδ_(eq)) Polyurethane mastic; 31.5 0.2 curve C1 (9 mm by 6 mm)Material A, curve C2 400 0.3 (15 mm by 3 mm) Material B and 70 0.95polyurethane mastic; curve C3 (15 mm by 6 mm)

The curves in FIG. 13 demonstrate the improved noise reduction achievedthanks to the strip of the invention. In this figure, the noiseexpressed in dB is plotted as a function of the engine speed in rpm ofthe vehicle. The measured noise here is that generated within the 50-160Hz frequency range, these frequencies corresponding to solid-borne noiseand corresponding to an engine speed of 1500 to 5000 rpm with regard tothe given type, of automobile taken here as example.

It should be noted that the measurements are independent of the area ofthe glazing assemblies.

The results show that at a frequency of 110 Hz, corresponding to 3400rpm and at a normal speed on a freeway, the noise measured on theglazing assembly corresponding to curve C1 is much higher than the noisemeasured on the glazing assembly corresponding to curve C2 and even morecompared with that corresponding to curve C3; noise damping, of 4 dB and13 dB respectively, is thus obtained thanks to the strip of theinvention according to one of the two versions respectively, as may beseen also from the graph in FIG. 12.

It may be preferable to use the strip corresponding to curve C2, as thisexhibits good damping performance at 3400 rpm and also exhibits goodperformance for a speed above 4000 rpm, for which it may be seen thatthe measured noise is 82 dB, whereas the measured noise corresponding tocurve C1 with a standard strip is 87 dB. This result is obtained sincethe equivalent real stiffness per unit length of this strip of theinvention is much greater than that of the standard strip.

The strip of the invention with acoustic damping properties has beendescribed by way of example for the case in which it is inserted betweentwo elements 1 and 2, such as a glass substrate and an automobile body,for the purpose of bonding one to the other, and therefore for aglass-metal joint. Other applications may be envisioned for the use ofthe acoustic damping strip of the invention, for example formetal-metal, glass-glass, metal-plastic, glass-plastic andplastic-plastic joints. The term “plastic” is understood to meanplastics such as an epoxy, a polyester, a polycarbonate, a polymethylmethacrylate (PMMA) or an acrylonitrile-butadiene-styrene resin, orcomposites based on a plastic, such as polypropylene (PP), andreinforcing fibers, such as glass fibers or wood fibers.

An example of a metal-metal joint is that of metal parts bonded to thebodywork of a vehicle. Thus, the mechanical components for opening thedoors and windows that are normally attached by means of bolts mayinstead be attached by bonding using a damping strip of the invention inorder to attenuate the radiation of noise into the passenger compartmentof the vehicle.

An example of a glass-plastic joint is that obtained when bonding a rearwindow of a vehicle.

An example of a plastic-plastic or plastic-metal joint is that obtainedwhen bonding the various elements that make up the tailgate of anautomobile, or else the adhesive bonding of a roof based on apolyurethane foam reinforced with glass fibers to the metal body of thevehicle.

1. A strip (3) to be inserted between two elements (1, 2) in order tocause acoustic attenuation of the noise propagating through at least oneof the elements, the strip (3) being formed from at least oneplastic-based damping material i, characterized in that the strip (3)has an equivalent real stiffness per unit length K′_(eq) equal to atleast 25 MPa and an equivalent loss factor tan δ_(eq) equal to at least0.25.
 2. The strip as claimed in claim 1, characterized in that it hasan equivalent real stiffness per unit length K′_(eq) of between 30 MPaand 270 MPa and an equivalent loss factor tan δ_(eq) equal to at least0.4.
 3. The strip as claimed in either of the preceding claims,characterized in that the strip (3) is formed from a single dampingmaterial (4) or from several damping materials (4 a, 4 b; 40, 41; 42,43; 44, 45; 46, 47).
 4. The strip as claimed in claim 3, characterizedin that the damping material or materials exhibit adhesion propertieswith respect to the two elements (1, 2).
 5. The strip as claimed inclaim 1 or 2, characterized in that the strip (3) is formed from atleast one damping material (4) and from a nondamping adhesive material,the adhesive material being designed to bond the two elements (1, 2)together.
 6. The strip as claimed in claim 5, characterized in that theadhesive material (5) adheres via two opposed faces (50, 51) to the twoelements (1, 2) respectively, the damping material being bonded to atleast one of the two elements.’
 7. The strip as claimed in claim 5,characterized in that the adhesive material (5) adheres via one of itsfaces (50) to the damping material (4) that is bonded to one of theelements (1) and adheres via its opposite face (51) to the other element(2) to be joined together.
 8. The strip as claimed in any one of claims3 to 7, characterized in that the strip (3) comprises several dampingmaterials (4 a, 4 b; 40, 41; 44, 45; 46, 47) placed as a stack of layersone on top of another, each of the materials at the ends of the stackbeing bonded to one of the two elements (1, 2) to be joined together orto the adhesive material (5).
 9. The strip as claimed in any one ofclaims 3 to 7, characterized in that the strip (3) comprises severaldamping materials (4 c, 4 d; 42, 43) placed in juxtaposition one besideanother, butted together or otherwise, each of the. materials having twoopposed surfaces bonded to the two elements (1, 2) to be joinedtogether, respectively.
 10. The strip as claimed in claims 8 and 9,characterized in that the strip (3) comprises several damping materialsplaced as a stack and in juxtaposition, at least one or two materialspartly constituting this combination being bonded to the two elements(1, 2) to be joined together.
 11. The strip as claimed in one of claims5 to 10, characterized in that the adhesive material (5) is placed so asto be stacked with and/or in juxtaposition with the damping material ormaterials.
 12. The strip as claimed in any one of claims 5 to 11,characterized in that the damping material or materials, together orwith the adhesive material (5), are separated by an air space (6). 13.The strip as claimed in any one of claims 5 to 12, characterized in thatthe nondamping adhesive material (5) is a polyurethane mastic having aYoung's modulus E′ of 21 MPa and a loss factor tan δ of 0.2.
 14. Thestrip as claimed in any one of the preceding claims, characterized inthat the damping material or materials are chosen from the followingplastics: plasticized or unplasticized polyvinyl chloride; thermoplasticelastomers; one-component or two-component polyurethanes possiblymodified by an elastomer, such as polyolefins, EPDM(ethylene-propylene-diene) or rubber, especially butyl rubber or nitrilerubber or else styrene-butadiene rubber; polyalkyl acrylate ormethacrylate copolymers; and epoxy resins.
 15. The strip as claimed inclaim 15, characterized in that the plastic contains organic or mineralfillers, such as talc, silica, calcium carbonate, kaolin, alumina,molecular sieve, carbon black, graphite and pyrogenic silica, or metalfillers.
 16. The strip as claimed in claim 15, characterized in that thedamping material is a one-component polyurethane that has an NCOpercentage content of between 0.5 and 2% and comprises: at least onepolyesterpolyol with a functionality of two (preferably between 80 and200 g), having an OH index iOH of between 5 and 10, a glass transitiontemperature T_(g) of −50° C. or below and a softening point between 50and 80° C.; at least one polyesterpolyol with a functionality of two(preferably between 120 g and 220 g), having an index iOH between 50 and100 and a glass transition temperature T_(g) of −50° C. or below; atleast one isocyanate with a functionality of between 2.1 and 2.7 of thediphenylmethane diisocyanate (MDI) type and having an NCO percentagecontent of between 11 and 33% (preferably between 180 and 220 g); atleast one catalyst (preferably between 0.5 and 3 g); optionally, afiller of the molecular sieve type (preferably between 20 and 60 g); andoptionally, at least one filler of the chalk, kaolin, talc, alumina,carbon black or graphite type (preferably between 5 and 60 g).
 17. Thestrip formed from the single damping material as claimed in claim 17,characterized in that it has, at 20° C., with a reference cross sectionof 15 mm in width and 3 mm in thickness, an equivalent real stiffnessper unit length of 400 MPa and an equivalent loss factor of 0.3.
 18. Thestrip as claimed in claim 15, characterized in that the damping materialis a one-component polyurethane that has an NCO percentage content ofbetween 0.5 and 2% and comprises: at least one polyesterpolyol with afunctionality of two (preferably between 350 and 450 g), having an OHnumber between 20 and 40 and a glass transition temperature T_(g) ofbetween −40 and −20° C.; at least one polyesterpolyol with afunctionality of two, having an OH number between 30 and 90 (preferablybetween 35 and 250 g), a glass transition temperature T_(g) between 0and 30° C. and a softening point between 50 and 70° C.; at least oneisocyanate having a functionality between 2.1 and 2.7 of thediphenylmethane diisocyanate (MDI) type and an NCO percentage content ofbetween 11 and 33% (preferably between 150 and 230 g); at least onecatalyst (preferably between 0.5 and 3 g); optionally, a filler of themolecular sieve type (preferably between 20 and 80 g); and optionally,at least one filler of the chalk, kaolin, talc, alumina, carbon black orgraphite type (preferably between 5 and 60 g).
 19. The strip formed as astack of the damping material as claimed in claim 19 and of a nondampingadhesive material of the polyurethane mastic type, characterized in thatit has, at 20° C., with a cross section of 15 mm in width and 3 mm inthickness for each of the two materials, an equivalent real stiffnessper unit length of 70 MPa and an equivalent loss factor of 0.95.
 20. Thestrip as claimed in claim 15, characterized in that the damping materialis a polyurethane prepolymer that has an NCO percentage content ofbetween 0.5 and 2%, the material comprising: at least onepolyetherpolyol with a functionality of two, having an index iOH ofbetween 25 and 35, a glass transition temperature T_(g) below −50° C.and a molecular mass between 3500 and 4500; at least one polyetherpolyolwith a functionality of between 2.3 and 4, having an index iOH between25 and 800 and a glass transition temperature T_(g) below −50° C.; atleast one polyesterpolyol with a functionality of two, having an indexiOH between 20 and 40 and a glass transition temperature T_(g) between40 and −20° C.; at least one polyesterpolyol with a functionality oftwo, having an index iOH between 30 and 90, a glass transitiontemperature T_(g) between 0 and 30° C. and a softening point between 50and 70° C.; at least one isocyanate with a functionality of between 2.1and 2.7 of the diphenylmethane diisocyanate (MDI) type and an NCOpercentage content between 11 and 33%; at least one catalyst;optionally, a filler of the molecular sieve type; and optionally, afiller of the chalk, kaolin, talc, alumina, carbon black or graphitetype.
 21. The strip as claimed in claim 20, characterized in that itcomprises, the NCO % content being between 1.8 and 2.2%: between 180 and220 g of a polyetherpolyol with a functionality of two, having an indexiOH between 25 and 35, a glass transition temperature T_(g) below −50°C. and a molecular mass between 3500 and 4500; between 75 and 115 g ofan isocyanate of the MDI type having an NCO % content equal to 11.9%;between 5 and 30 g of carbon black; between 0.5 and 3 g of catalyst;between 10 and 30 g of pyrogenic silica; between 135 and 180 g of aliquid and amorphous polyesterpolyol A with an index iOH between 27 and34, a molecular mass of 3500, a functionality of two and a glasstransition temperature T_(g) of −30° C.; between 35 and 85 g of a liquidand amorphous polyesterpolyol B with an index iOH between 27 and 34, amolecular mass of 3500, a functionality of two and a glass transitiontemperature T_(g) of +20° C., respectively; between 55 and 110 g of anMDI-type isocyanate, with an NCO % content of 11.9%; and between 20 and80 g of molecular sieve.
 22. The strip formed from the single dampingmaterial as claimed in claim 20 or 21, characterized in that it has, at20° C., with a reference cross section of 15 mm in width and 3 mm inthickness, an equivalent real stiffness per unit length of 120 MPa andan equivalent loss factor of 0.75.
 23. The strip as claimed in any oneof the preceding claims, characterized in that it is applied to at leastone of the elements by a process of extrusion, and/or of encapsulation,and/or of transfer from a molding, and/or of injection molding.
 24. Thestrip as claimed in any one of the preceding claims, characterized inthat the strip has a uniform or nonuniform cross section over all orpart of its length.
 25. The strip as claimed in any one of claims 1 to21, characterized in that it is joined to two elements (1, 2) of themetal-metal, glass-glass, metal-plastic, plastic-glass orplastic-plastic type.
 26. The strip as claimed in claim 22,characterized in that it is inserted between a glass substrate and ametal element so as to be used for attaching the substrate to the metalelement.
 27. The strip as claimed in claim 23, characterized in that itis used for the attachment of glazing to the body of a motor vehicle.28. The strip as claimed in claim 24, characterized in that the glazingconsists of a laminated glazing assembly comprising at least two glasssheets and a film with acoustic properties.
 29. A method of evaluatingthe acoustic damping properties of a strip designed to be insertedbetween two elements formed from at least one damping material i,characterized in that it consists in evaluating the equivalent realstiffness per unit length K′_(eq) of the strip and the equivalent lossfactor tan δ_(eq), the strip having acoustic damping properties when theequivalent real stiffness per unit length is at least equal to 25 MPaand the equivalent loss factor is at least 0.25.
 30. The method asclaimed in claim 26, characterized in that the evaluation of theequivalent real stiffness per unit length K′_(eq) of the strip and ofthe equivalent loss factor tan δ_(eq) comprises steps of measuring theYoung's modulus E_(i)′ and the loss modulus E_(i)″ of each constituentmaterial i of the strip and steps of calculating using the formulae:$\begin{matrix}{\left\lbrack K_{eq}^{*} \right\rbrack^{\alpha} = {\sum\left\lbrack K_{i}^{*} \right\rbrack^{\alpha}}} & (1) \\{K_{i}^{*} = {E_{i}^{*} \times \frac{L_{i}}{e_{i}}}} & (2) \\{{\tan\quad\delta_{eq}} = \frac{K_{eq}^{''}}{K_{eq}^{\prime}}} & (3)\end{matrix}$ where L_(i) and e_(i) are the width and the thickness ofthe material, respectively.
 31. The method as claimed in claim 27,characterized in that the Young's modulus E_(i)′ and the loss modulusE_(i)″ of each constituent material i of the strip are measured by meansof a viscoanalyzer.
 32. The method as claimed in claim 26, characterizedin that the viscoanalyzer is used to make-direct measurements of theequivalent real stiffness k′_(eq) and the equivalent loss modulusk″_(eq) of a strip specimen with a cross section identical to that ofthe strip and with a length L and then the following are calculated: theratio of the measured equivalent real stiffness to the length L in orderto obtain the equivalent real stiffness per unit length K′_(eq) of thestrip: K′_(eq)=k′_(eq)/L; and the ratio of the measured equivalent lossfactor to the measured equivalent real stiffness in order to obtain theequivalent loss factor tan δ_(eq) of the strip:$\frac{k_{eq}^{''}}{k_{eq}^{\prime}}.$